Electron-emitting element, fluorescent light-emitting element, and image displaying device

ABSTRACT

A principal object of the present invention is to provide efficiently an electron-emitting element demonstrating performance equal or superior to that attained with the conventional technology. The electron-emitting element of the present invention comprises: (a) a substrate, (b) a lower electrode layer provided on the substrate, (c) an electron-emitting layer provided on the lower electrode layer, and (d) a control electrode layer so disposed as not to be in contact with the electron-emitting layer, wherein the electron-emitting layer comprises an electron-emitting material for emitting electrons in an electric field, (1) the electron-emitting material being a porous body having a 3D-network structure skeleton, (2) the 3D-network structure skeleton being composed on an inner portion and a surface portion, (3) the surface portion comprising an electron-emitting component, (4) the inner portion being occupied by (i) at least one of an insulating material and a semiinsulating material, (ii) an empty space, or (iii) at least one of an insulating material and a semiinsulating material and an empty space.

TECHNICAL FIELD

The present invention relates to an electron-emitting element, afluorescent light-emitting element, and an image displaying device,using an electron-emitting material having a three dimensional network(3D-network) skeleton as an electron-emitting layer.

BACKGROUND ART

Electron emission effects from the solid surfaces include: (1)thermionic emission in which electrons are emitted due to heat, and (2)field electron emission in which electrons are emitted due to electricfield. In recent years, cold cathode emitters of a field emission type(FE emitters) which do not require heating have attracted attention. Forexample, Spindt-type and thin-film emitters are known as such FEemitters.

Spindt-type electron-emitting elements are the basic type of FEemitters. The operation thereof is based on causing the emission ofelectrons in vacuum by applying a high electric field (>1×10⁹ V/m) to adistal end region of a fine conical emitter tip formed from a metalmaterial with a high melting point, such as silicon (Si) and molybdenum(Mo) (see, for example, U.S. Pat. No. 3,665,241).

A thin-film electron-emitting element represents the development of theSpindt-type electron-emitting element. Thin-film electron-emittingelements do not use the fine conical structure typical for theSpindt-type elements and electrons are emitted from a flat emitter. Inthis element, because the emitter has a flat shape, an electric fieldconcentration effect obtained with the conical structure cannot beexpected. For this reason, a limitation is placed on the emittermaterials that can be used in the thin-film electron-emitting elements.

Carbon materials such as amorphous carbon films, diamond, and carbonnanotubes (CNT) are known as materials for emitters (for example, see,Japanese Unexamined Patent Publication Nos. H8-505259, H7-282715, andH10-012124). Among the aforementioned carbon materials, CNT is a finetubular material (diameter in the order of several to several tens ofnanometer) having a shape in which a graphen sheet composed only ofcarbon is wound into a cylinder. This material is electricallyconductive and has a sharp form with a large aspect ratio. For thisreason, it is the most promising as an effective emitter material amongall the carbon materials.

Furthermore, a field electron-emitting element is known which comprisesan emitter electrode for emitting electrons under applied electricfield, an electron accelerating layer, and an extraction electrode,wherein the electron accelerating layer is composed of a porous silicafilm (Japanese Unexamined Patent Publication No. 2000-285797). Amaterial obtained by precipitating graphite or silicon inside pores isused as the porous silica film, but it is assumed that it will bedisposed in contact with the extraction electrode.

DISCLOSURE OF THE INVENTION

In the Spindt-type electron-emitting element, electrons are emitted byan electric field concentration effect relating to a distal end portionof a sharp conical structure by using a semiconductor process. For thisreason, characteristics of such an element are greatly affected by theshape of the distal end or surface state. Therefore, stable desiredcharacteristics are difficult to obtain. Furthermore, the aforementionedprocess places a limitation on the materials that can be used. Moreover,a display with a large surface area is difficult to produce from suchelements.

By contrast, in the thin-film electron-emitting element, it is not thatnecessary to conduct strict control of the emitter portion, unlike theSpindt-type electron-emitting element. For this reason, thin-filmelectron-emitting elements seem to be superior to the Spindt-typeelectron-emitting elements in terms of stability and increase in surfacearea. However, as described above, the number of emitter materials whichhave desired characteristics is limited. Thus, they cannot be used asemitter materials unless the properties or microstructure thereof arecontrolled.

As described above, a variety of carbon materials have been studied aspromising candidates for the emitter materials, but in materials otherthan CNT, sufficient characteristics have not yet been obtained. Forthis reason, it was necessary to rely on CNT as the emitter material.

However, the CNT which are presently considered as an optimum materialare expensive and can hardly be considered as a material suitable forthe manufacture on an industrial scale. Another problem associated withthe CNT is that they are in a powdered form and are therefore difficultto handle.

Therefore, it is a main object of the present invention to resolve theabove-described problems inherent to the related technology and toprovide effectively an electron-emitting element demonstrating excellentperformance equal or superior to that of the related technology.

Thus, the present invention relates to the below-describedelectron-emitting element, fluorescent light-emitting element, and imagedisplaying device.

1. An electron-emitting element comprising: (a) a substrate, (b) a lowerelectrode layer provided on said substrate, (c) an electron-emittinglayer provided on said lower electrode layer, and (d) a controlelectrode layer so disposed as not to be in contact with saidelectron-emitting layer,

-   -   wherein said electron-emitting layer comprises an        electron-emitting material for emitting electrons in an electric        field;    -   (1) said electron-emitting material being a porous body having a        3D-network structure skeleton, (2) the 3D-network structure        skeleton being composed of an inner portion and a surface        portion, (3) the surface portion comprising an electron-emitting        component, (4) the inner portion being occupied by (i) at least        one of an insulating material and a semiinsulating        material, (ii) an empty space, or (iii) an empty space and at        least one of an insulating material and a semiinsulating        material.

2. The electron-emitting element according to above 1, wherein saidelectron-emitting material is exposed on the surface of saidelectron-emitting layer.

3. The electron-emitting element according to above 2, wherein saidelectron-emitting layer consist of an electron-emitting material foremitting electrons in an electric field.

4. The electron-emitting element according to above 1, wherein saidelectron-emitting layer has electric conductivity.

5. The electron-emitting element according to above 1, wherein saidelectron-emitting layer is obtained by baking a coating film of a pastecontaining a powdered electron-emitting material.

6. The electron-emitting element according to above 1, wherein thesubstantially entire inner portion is composed of an inorganic oxide.

7. The electron-emitting element according to above 1, wherein thesubstantially entire inner portion is composed of an empty space.

8. The electron-emitting element according to above 1, wherein theelectron-emitting component is a carbon material.

9. The electron-emitting element according to above 8, wherein thecarbon material has one or more π bonds.

10. The electron-emitting element according to above 8, wherein thecarbon material contains graphite as the main component.

11. A fluorescent light-emitting element comprising an anode portionhaving a fluorescent layer and an electron-emitting element, said anodeportion and electron-emitting element being so disposed that theelectrons emitted from said electron-emitting element cause saidfluorescent layer to emit light, wherein said electron-emitting elementis the element according to above 1.

12. An image displaying device comprising an anode portion having afluorescent layer and a plurality of electron-emitting elements disposedtwo-dimensionally, said anode portion and electron-emitting elementsbeing so disposed that the electrons emitted from said electron-emittingelements cause said fluorescent layer to emit light, wherein saidelectron-emitting element is the element claimed in above 1.

13. A method for manufacturing an electron-emitting material, (1) theelectron-emitting material being a porous body having a 3D-networkstructure skeleton, (2) the 3D-network structure skeleton being composedon an inner portion and a surface portion, (3) the surface portioncomprising an electron-emitting component, (4) the inner portion beingcomposed of (i) at least one of an insulating material and asemiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial,

-   -   wherein the method comprises a step A of obtaining an        electron-emitting material composed of a carbon-containing        material by adding a carbon material to a gel of an inorganic        oxide having a 3D-network structure skeleton.

14. The manufacturing method according to above 13, further comprising astep of removing the inorganic oxide partially or entirely from thecarbon-containing material.

15. The manufacturing method according to above 13, wherein a dry gel isused as the gel of the inorganic oxide and the step of obtaining aporous body as the carbon-containing material by adding a carbonmaterial to the dry gel is implemented as the step A.

16. The manufacturing method according to above 13, wherein the carbonprecursor contains an organic polymer.

17. The manufacturing method according to above 14, wherein a carbonprecursor contains an organic polymer.

18. The manufacturing method according to above 16, wherein the organicpolymer has one or more carbon-carbon unsaturated bonds.

19. The manufacturing method according to above 16, wherein the organicpolymer has one or more aromatic rings.

20. The manufacturing method according to above 16, wherein the organicpolymer is at least one of phenolic resins, polyimides, andpolyacrylonitrile.

21. A method for manufacturing an electron-emitting material, (1) theelectron-emitting material being a porous body having a 3D-networkstructure skeleton, (2) the 3D-network structure skeleton being composedof an inner portion and a surface portion, (3) the surface portioncomprising an electron-emitting component, (4) the inner portion beingcomposed of (i) at least one of an insulating material and asemiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial,

-   -   wherein the method comprises a step B of obtaining an        electron-emitting material composed of a carbon-containing        material by adding a carbon precursor to a gel of an inorganic        oxide having a 3D-network structure skeleton and carbonizing the        carbon precursor containing gel thus obtained.

22. The manufacturing method according to above 21, further comprising astep of removing the inorganic oxide partially or entirely from thecarbon precursor containing gel.

23. The manufacturing method according to above 21, wherein a wet gel isused as the gel of the inorganic oxide and a step of obtaining a porousbody as the carbon-containing material by adding a carbon precursor tosaid wet gel and drying the carbon precursor containing gel thusobtained to obtain a carbon precursor containing dry gel, and thencarbonizing said dry gel is carried out as the step B.

24. The manufacturing method according to above 22, wherein a wet gel isused as the gel of the inorganic oxide and a step of obtaining a porousbody as the carbon-containing material by adding a carbon precursor tosaid wet gel, removing the inorganic oxide partially or entirely fromthe carbon precursor containing gel thus obtained, and then carbonizingthe obtained material is carried out as the step B.

25. The manufacturing method according to above 21, wherein the carbonprecursor contains an organic polymer.

26. The manufacturing method according to above 22, wherein the carbonprecursor contains one or more types of organic polymer.

27. The manufacturing method according to above 25, wherein the organicpolymer has one or more carbon-carbon unsaturated bonds.

28. The manufacturing method according to above 25, wherein the organicpolymer has one or more aromatic rings.

29. The manufacturing method according to above 25, wherein the organicpolymer is at least one of phenolic resins, polyimides, andpolyacrylonitrile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematic drawing illustrating a model of a fine structure of a3D-network structure skeleton;

FIG. 2 a schematic drawing illustrating a 3D-network skeleton compositestructure having an electron-emitting component film.

FIG. 3 a schematic drawing illustrating an electron-emitting componentstructure composed having a 3D-network skeleton, wherein the skeleton ishollow;

FIG. 4 a schematic drawing illustrating an example of the manufacturingprocess in accordance with the present invention;

FIG. 5 a schematic drawing illustrating an example of the manufacturingprocess in accordance with the present invention;

FIG. 6 a schematic drawing illustrating an example of the manufacturingprocess in accordance with the present invention;

FIG. 7 a schematic drawing illustrating an example of the manufacturingprocess in accordance with the present invention;

FIG. 8 is a schematic cross-sectional view of the electron-emittingelement in accordance with the present invention;

FIG. 9 is a schematic cross-sectional view of the fluorescentlight-emitting element using the electron-emitting element;

FIG. 10 is a cross-sectional perspective view of an image displayingdevice in which a plurality of electron-emitting elements are arrangedtwo dimensionally; and

FIG. 11 illustrates schematically a conventional element emittingelectrons in electric field.

KEYS

-   10 GEL STRUCTURE (POROUS BODY)-   11 FINE PARTICLES-   12 FINE PORES-   13 DENDRITIC DIAGRAM REPRESENTING A 3D-NETWORK SKELETON-   20 ELECTRON-EMITTING MATERIAL (COMPOSITE STRUCTURE OF    ELECTRON-EMITTING COMPONENT FILM)-   21 ELECTRON-EMITTING COMPONENT-   22 INSULATING MATERIAL (OR SEMIINSULATING MATERIAL)-   30 ELECTRON-EMITTING MATERIAL (HOLLOW ELECTRON-EMITTING MATERIAL    STRUCTURE)-   31 ELECTRON-EMITTING COMPONENT-   32 HOLLOW SPACE-   80 ELECTRON-EMITTING ELEMENT-   81 SUBSTRATE-   82 ELECTRODE LAYER-   83 ELECTRON-EMITTING LAYER-   84 CONTROL ELECTRODE LAYER-   85 INSULATING LAYER-   86 CONTROL POWER SOURCE-   87 PROTRUDING PORTION-   88 SPACE REGION-   90 ELECTRON-EMITTING ELEMENT-   91 SUBSTRATE-   92 ELECTRODE LAYER-   93 ELECTRON-EMITTING LAYER-   94 CONTROL ELECTRODE LAYER-   95 INSULATING LAYER-   96 CONTROL POWER SOURCE-   100 ANODE PORTION-   97 FLUORESCENT BODY LAYER-   98 ANODE ELECTRODE LAYER-   99 FRONT SUBSTRATE-   910 ACCELERATING POWER SOURCE-   911 VACUUM CONTAINER-   101 SUBSTRATE-   102 ELECTRODE LAYER-   103 ELECTRON-EMITTING LAYER-   104 CONTROL ELECTRODE LAYER-   105 FLUORESCENT LAYER-   106 ANODE ELECTRODE LAYER-   107 FRONT SUBSTRATE-   108, 109 OPERATING DRIVER-   201 POROUS SILICA FILM-   202 ELECTRICALLY CONDUCTIVE SUBSTRATE-   203 UPPER ELECTRODE.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Electron-Emitting Element

The electron-emitting element of the present invention is anelectron-emitting element comprising: (a) a substrate, (b) a lowerelectrode layer provided on the substrate, (c) an electron-emittinglayer provided on the lower electrode layer, and (d) a control electrodelayer so disposed as not to be in contact with the electron-emittinglayer,

wherein the electron-emitting layer comprises an electron-emittingmaterial for emitting electrons in an electric field,

(1) the electron-emitting material being a porous body having a3D-network structure skeleton, (2) the 3D-network structure skeletonbeing composed of an inner portion and a surface portion, (3) thesurface portion comprising an electron-emitting component, (4) the innerportion being composed of (i) at least one of an insulating material anda semiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial.

First, the electron-emitting material constituting the electron-emittinglayer of the element in accordance with the present invention and themethod for manufacture thereof will be described.

(1) Electron-Emitting Material and Method for Manufacture Thereof

(1-1) Electron-Emitting Material

The electron-emitting material in accordance with the present invention(will be also referred to hereinbelow as “material in accordance withthe present invention”) emits electrons in an electric field. Morespecifically, a material satisfying the following four conditions isused.

The electron-emitting material: (1) is a porous body having a 3D-networkstructure skeleton, (2) the 3D-network structure skeleton is composed onan inner portion and a surface portion, (3) the surface portioncomprises an electron-emitting component, (4) the inner portion isoccupied by (i) at least one of an insulating material and asemiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial.

No limitation is placed on the shape or size of the electron-emittingmaterial and they may be appropriately determined according to theapplication or object of use. Further, the material in accordance withthe present invention may be subjected to comminuting, provided the fouraforementioned conditions are satisfied. For example, the materials inaccordance with the present invention also include a powder with a meanparticle size of 0.5 μm or more and 50 μm or less.

[Porous Body]

The 3D-network structure skeleton of the porous body mentioned above maybe a skeleton with a three-dimensional 3D-network structure. Thisskeleton preferably has multiple pores. In the preferred skeleton, finesolid components (linear bodies) having a size of about 2 to 30 nm areintertwined as a 3D-network configuration, and the gaps therebetween areempty. The porous body is a solid substance having continuous orindividual fine pores. Such a body can be produced by a variety ofmethods such as molding of a starting material powder, sintering thepowder, chemical foaming, physical foaming, and sol-gel process, asdescribed hereinbelow.

The bulk density, BET specific surface area, and mean pore size of theporous body can be appropriately determined by the type of theinsulating material, application of the porous body, and method of use.The bulk density may be appropriately determined usually from within arange of 10 to 500 kg/m³, in particular, 50 to 400 kg/m³. The specificsurface area can be appropriately set usually from within a range ofabout 50 to 1500 m²/g, in particular, 100 to 1000 m³/g. The specificsurface area is a value measured by a Brunauer-Emmet-Teller method(abbreviated below as “BET method”) which is a nitrogen adsorptionmethod. Furthermore, the mean pore diameter of the porous body can beappropriately determined usually from within a range of 1 to 1000 nm, inparticular, 5 to 50 nm.

[Surface Portion of Porous Body]

The surface portion comprises an electron-emitting component. Theelectron-emitting component may be any component capable of emittingelectrons in an electric field (field emission function). It isespecially preferred that semiconductor materials with a wide band gapand materials with a small work function (small electron affinity) beused.

Examples of specific materials include alkali metals such as cesium andoxides thereof; alkaline earth metals such as beryllium, calcium,magnesium, strontium, barium, and oxides thereof; carbon materials suchas carbon blacks (e.g. acetylene blacks and ketjen blacks), activecarbon, artificial graphite, natural graphite, carbon fibers, pyrolyzedcarbon, glassy carbon, impermeable carbon, special carbon, and coke;nitrides such as aluminum nitride and boron nitride; and mixed-crystalmaterials thereof. These materials may used singly or in combination oftwo or more thereof.

Among them, carbon materials are especially preferred. Carbon materialsmay be crystalline or amorphous. When the carbon material iscrystalline, no specific limitation is placed on the crystal structurethereof. For example, it may have a diamond structure or a graphitestructure. Moreover, carbon nanotubes, carbon nanohorns, carbonnanoribbons, carbon nanocoils, and carbon nanocapsule can be also usedas the carbon material.

A carbon material produced by carbonization of starting materials forthe carbon material and/or a carbon material obtained by carbonizationof an organic polymer serving as a carbon precursor are preferably usedas the aforementioned carbon material. The advantage of such materialsis that they can be readily formed on the gel skeleton surface and thatcarbon structure and properties can be freely controlled by changing theformation conditions, carbonization conditions or the like.

In the surface portion, in particular, in a state called a negativeelectron affinity (NEA) or a state with an extremely small positiveelectron affinity, the energy level at the edge of the conduction bandwhere electrons can be present is higher than or the same as the vacuumlevel. As a result, the electrons can be very easily emitted from theelectron-emitting surface into vacuum.

The thickness of the surface portion can be appropriately determinedaccording to the type of the electron-emitting component. Usually it isabout 3 to 100 nm, preferably 3 to 20 nm. This thickness can becontrolled by changing the conditions of the below-describedmanufacturing process.

[Inner Portion of Porous Body]

The inner portion is occupied by (i) at least one of an insulatingmaterial and a semiinsulating material, (ii) an empty space, or (iii) atleast one of an insulating material and a semiinsulating material (bothare referred to hereinbelow as “insulating material”) and an emptyspace.

Thus, in the porous body, the content (occupation ratio) of theinsulating material in the inner portion of the porous body is within arange of 0 vol. % or more to 100 vol. % or less. Therefore, the scope ofthe present invention includes the following cases: (i) the innerportion of the porous body is substantially entirely formed from aninsulating material, (ii) the inner portion of the porous body issubstantially entirely an empty space (hollow portion), and (iii) partof the inner portion of the porous body is an insulating material andthe remaining part is an empty space.

The insulating material can be selected from well-known insulatingmaterials or semiinsulating materials. Typically, electric conductivitythereof may be 10⁻³ S/cm or less (27° C.).

In particular, in accordance with the present invention, it is preferredthat inorganic oxides be used because the can easily form a porous bodyhaving a 3D-network structure skeleton. Examples of suitable inorganicoxides include silicon oxide, aluminum oxide, titanium oxide, vanadiumoxide, iron oxide, zirconium oxide, and magnesium oxide, mixtures (mixedoxides) thereof, and composite oxides. Those oxides can be used singlyor in combinations of two or more thereof.

Further, in cases above (i) and (iii), the ratio of the insulatingmaterial and electron-emitting component can be appropriately determinedaccording to the type of the insulating material or electron-emittingcomponent and the application of the porous body.

EMBODIMENT 1

The preferred embodiment of the electron-emitting material will bedescribed hereinbelow with reference to the drawings. In accordance withthe present invention, no specific limitation is placed on the methodfor forming a porous body having a 3D-network structure skeleton. Amongsuch methods, a sol-gel method is described as the preferred workingexample of the present invention because it is a simple method.Therefore, the explanation will be focused on the process employing asol-gel method.

FIG. 1(a) illustrates schematically the microstructure of a porous body10 (a 3D-network skeleton structure body having a multiplicity of finepores) produced by a sol-gel method. In this porous body, aggregates offine particles 11 having a diameter of 2 to 30 nm are combined togetherin a three-dimensional network to form a porous structure comprising alarge number of fine pores (vapor phase) 12 with a size of 1 μm or less,while maintaining a solid shape. As a result, a low-density body with aporosity of 50% or more can be obtained and, therefore, a porousstructure with a large specific surface area can be obtained. Forexample, a porous body with a specific surface area measured by BETmethod of 100 m²/g or more can be obtained.

In FIG. 1(b), the connection state of solid portions (skeleton portions)of the porous body shown in FIG. 1(a) is represented with lines. It isclear that the skeleton portion has a 3D-network structure composed of arandom network.

FIG. 1(c) is a diagram obtained by extracting only the linesrepresenting the 3D-network skeleton, based on FIG. 1(b). The porousstructure composed of associations of fine particles will be simulatedby such dendritic lines 13.

FIG. 1 illustrates an example of a porous structure composed of fineparticle associations, but the present invention is not limited to thisexample. For example, porous structures having a multiplicity of finepores, such as an association of linear substances and a structure inwhich beehive holes are opened in a larger structural body may be used.Any reference made hereinbelow to the structure depicted in FIG. 1(c)will be assumed to include those structures.

EMBODIMENT 2

FIG. 2 shows the preferred embodiment of the electron-emitting material.The first configuration of a material 20 in accordance with the presentinvention represents a structure 21 composed of a fine 3D-networkskeleton, such as shown in FIG. 2, with a coating of anelectron-emitting component. Thus, a 3D-network skeleton composed of aninsulating material (or semiinsulating material) 22 is employed as acore and the surface of the skeleton is coated with an electron-emittingcomponent 21.

EMBODIMENT 3

A second configuration of the electron-emitting material in accordancewith the present invention is shown in FIG. 3. This material is composedof a 3D-network skeleton structure and is an electron-emitting material30 composed of an electron-emitting component 31, wherein the innerportion of the skeleton is a hollow space 32. Thus, this material has astructure composed of intertwined tubular skeletons.

In this structure, the inner portion of the 3D-network skeletonstructure is the hollow space 32. Therefore, the specific surface areais higher than that when no hollow space is present. Thus, theperformance can be further improved with respect to that provided for bythe 3D-network skeleton structure. As a result, such a material issuitable for applications requiring higher electron emission capability.

(1-2) Method for the Manufacture of Electron-Emitting Material

No specific limitation is placed on the method for the manufacture ofthe electron-emitting material. For example, when the insulatingmaterial and electron-emitting component are an inorganic oxide and acarbon material, respectively, the electron-emitting material can beadvantageously manufactured by the below-described first method andsecond method.

The first method is a method for the manufacture of an electron-emittingmaterial, (1) the electron-emitting material being a porous body havinga 3D-network structure skeleton, (2) the 3D-network structure skeletonbeing composed of an inner portion and a surface portion, (3) thesurface portion comprising an electron-emitting component, (4) the innerportion is composed of (i) at least one of an insulating material and asemiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial, wherein the method comprises at least (1) a step A ofobtaining a carbon-containing material by adding a carbon material to agel of an inorganic oxide having a 3D-network structure skeleton, or (2)a step B of obtaining a carbon-containing material by adding a carbonprecursor to a gel of an inorganic oxide having a 3D-network structureskeleton and carbonizing the carbon precursor containing gel thusobtained.

The second method is the above-described first method further comprisinga step of removing the inorganic oxide partially or entirely from thecarbon-containing material or a material containing a carbon precursor.

First Method

The first method is a manufacturing method comprising at least (1) astep A of obtaining a carbon-containing material by adding a carbonmaterial to a gel of an inorganic oxide having a 3D-network structureskeleton or (2) a step B of obtaining a carbon-containing material byadding a carbon precursor to a gel of an inorganic oxide having a3D-network structure skeleton and carbonizing the carbon precursorcontaining gel thus obtained.

With the first method, an electron-emitting material (porous body) canbe advantageously manufactured in which the inner portion of the porousbody is substantially entirely occupied by an inorganic oxide. With thefirst method, either the process A or process B is selectivelyimplemented.

[Process A]

Process A is a process for providing carbon to the aforementioned geland obtaining a carbon-containing material.

No limitation is placed on the inorganic oxide gel having a 3D-networkstructure skeleton, which is a starting material, provided it has a3D-network structure skeleton. Furthermore, depending on whether a gelcontains a liquid (solvent), there are two types of gels: a wet gel (agel containing a solvent in the gaps of the 3D-network structureskeleton) and a dry gel (gel in which substantially no solvent ispresent in the gaps of the 3D-network structure skeleton). Gels of bothtypes can be used in accordance with the present invention.

Furthermore, the type of inorganic oxide can be appropriately selectedfrom metal oxides of a variety of types according to the application ofthe electron-emitting material and method of use. In particular, inorder to form a 3D-network structure skeleton, it is especiallypreferred that the selected inorganic oxide can be formed by a sol-gelmethod. Examples of suitable compounds include silicon oxide (silica),aluminum oxide (alumina), titanium oxide, vanadium oxide, tantalumoxide, iron oxide, magnesium oxide, zirconium oxide, zinc oxide, tinoxide, cobalt oxide, and also mixed oxides and double oxides thereof.Among them at least one of silica and alumina is preferred because itallows a wet gel to be formed easily by a sol-gel method.

A gel manufactured by a known method can be used. In particular, asdescribed above, a gel prepared by a sol-gel method can be usedadvantageously because it allows a 3D-network structure skeleton to beformed with higher reliability. The explanation hereinbelow will beconducted with reference to the manufacture with the sol-gel method, asa representative example.

No limitation is placed on the starting materials, provided that a wetgel can be formed by a sol-gel reaction. Starting materials that havebeen used by the conventional sol-gel method can be used. For example,inorganic materials such as sodium silicate and aluminum hydroxide, andorganic materials of organometallic alkoxides such astetramethoxysilane, tetraethoxysilane, aluminum isopropoxide, andaluminum-sec-butoxide can be used. Those materials are selectedaccording to the type of the target inorganic oxide.

The sol-gel method can be performed under the well-known conditions.Typically a solution may be prepared by dissolving the aforementionedstarting materials in a solvent, conducting a reaction at roomtemperature or under heating, and gelling. For example, when a wet gelof silica (SiO₂) is produced, the method may be implemented as follows.

Examples of starting materials for silica include alkoxysilane compoundssuch as tetramethoxysilane, tetraethoxysilane, trimethoxymethylsilane,diethoxydimethylsilane, oligomers thereof, water glass compounds such assodium silicate (soda silicate) and potassium silicate, and colloidalsilica. They can be used singly or in mixture thereof.

No specific limitation is placed on the solvent, provided that startingmaterials can be dissolved therein and the silica produced is notdissolved therein. In addition to water, examples of suitable solventsinclude methanol, ethanol, propanol, acetone, toluene, and hexane. Thosesolvents can be used singly or in combination of two or more thereof.

If necessary, a variety of additives such as catalysts andviscosity-adjusting agents can be added. Water, acids such ashydrochloric acid, sulfuric acid, and acetic acid, and bases such asammonia, pyridine, sodium hydroxide, and potassium hydroxide can be usedas a catalyst. Ethylene glycol, glycerin, polyvinyl alcohol, andsilicone oil can be used as the viscosity-adjusting agents. Nolimitation is placed thereon, provided that the wet gel can be obtainedin a prescribed usage form.

A solution is prepared by dissolving the starting material in thesolvent. In this case, the concentration of the solution differsdepending on the type of starting materials or solvent used and thedesired state of the gel. Typically the concentration of solidcomponents forming the skeleton may be about 2 to 30 wt. %. With usingthe solution, a desired usage shape may be formed by injection molding,coating, or the like after optional addition of the aforementionedadditives and stirring. If the fixed time elapses in this state, thesolution is gelled and the prescribed wet gel can be obtained. Morespecifically, starting materials react in the solvent and form fineparticles and a wet gel is produced by the fine particles thatcongregate and form a 3D-network structure skeleton.

In this case no limitation is placed on the solution temperature, andthe process may be conducted at normal temperature or under heating. Incase of heating, the temperature can be appropriately set within atemperature range below the boiling point of the solvent used. Forcertain combinations of starting materials, cooling may be conductedduring gelling.

The wet gel produced may be subjected, if necessary, to surfacetreatment with the object of increasing affinity to a solvent insubsequent processing such as carbon precursor formation. In this case,the treatment can be conducted by inducing chemical reaction of asurface treatment agent with the surface of solid components in asolvent after the wet gel has been produced.

Examples of surface treatment agents include halogenated silanetreatment agents such as trimethylchlorosilane, dimethyldichlorosilane,methyltrichlorosilane, ethyltrichlorosilane, and phenyltrichlorosilane;alkoxysilane treatment agents such as trimethylmethoxysilane,trimethylethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane,and phenyltriethoxysilane; silicone silane treatment agents such ashexamethyldisiloxane and dimethylsiloxane oligomer, aminosilanetreatment agents such as hexamethyldisilazane, and alcohol-basedtreatment agents such as propyl alcohol, butyl alcohol, hexyl alcohol,octanol, and decanol. Those agents may be selected individually or incombination of two or more thereof according to the application of theelectron-emitting material (porous body).

As described above, carbon or materials containing carbon as the maincomponent can be used as the carbon material provided to the gel.Examples of suitable materials include carbon black (acetylene black,Ketjen black, and the like), active carbon, artificial graphite, naturalgraphite, carbon fibers, pyrolyzed carbon, glassy carbon, impermeablecarbon, special carbon, and coke. No limitation is placed on the crystalstructure, and diamond structure and graphite structure may be used.Furthermore, nanocarbon materials such as carbon nanotubes, carbonnanohorns, carbon nanoribbons, carbon nanocoils, and carbon nanocapsulescan be used. Those materials can be used singly or in combination or twoor more thereof. The materials can be appropriately selected accordingto the application of the porous body.

No limitation is placed on the method for providing the carbon material.A vapor phase method, liquid phase method, or solid phase method can beemployed. For example, (a) a method for depositing a carbon material onthe skeleton surface of the gel (preferably, dry gel) by a vapor phaseprocess, and (b) a method for providing a dispersion of a carbonmaterial (for example, carbon-containing ultrafine particles having anaverage particle size of 10 nm or less) to a gel (preferably, wet gel)can be employed.

A process for providing a carbon material by a vapor phase method willbe described as the method (a).

In this method, energy is imparted to a starting material that canproduce a carbon material, and the carbon material thus produced isdeposited on the gel skeleton surface. According to this method, acarbon material can be formed on the gel. Therefore, this method iseffective because it does not require a carbonization treatment to beconducted in the implementation thereof.

Examples of the aforementioned starting materials include saturatedhydrocarbon compounds such as methane, ethane, propane, and butane,unsaturated hydrocarbon compounds such as ethylene, acetylene, andpropylene, aromatic hydrocarbon compounds such as benzene and xylene,alcohols such as methanol and ethanol, nitrogen-containing hydrocarbonssuch as acrylonitrile, and carbon-containing gases such as gaseousmixture of carbon monoxide and hydrogen and gaseous mixtures of carbondioxide and hydrogen. Those starting materials can be used singly or incombination of two or more thereof.

Heat, plasma, ions, light, and catalysts can be employed as an energyfor converting those starting materials into carbon. A method comprisingheating is preferred for advancing carbonization in the dry gel becausethis method has high controllability.

The vapor phase method may be implemented under usual conditions. Forexample, a method may be used by which a gel is placed in a reactionvessels, the aforementioned starting materials are evaporated in thereactive atmosphere, and carbon is deposited on the gel skeleton surfaceunder heating. The conditions of this process can be appropriatelyadjusted according to the application and desired properties of theporous body.

With the aforementioned method (b), a wet gel is preferably used, and acarbon-containing material can be obtained by dispersing carbon in thesolvent contained in the gel and then conducting drying. In this case,the carbon material which is to be dispersed is preferably in the formof ultrafine particles having a mean particle size of 1 nm to 10 nm.

No specific limitation is placed on the amount (coated amount) of carbonmaterial used when the carbon material is coated on the gel. This amountcan be appropriately set according to the application of theelectron-emitting material, method of use, and type of the carbonmaterial used.

The carbon-containing material obtained in the process A may be used asis as the electron-emitting material. Furthermore, a solvent removalprocess (drying process) may be also implemented, if necessary, with theobject of removing the remaining solvent present in the gel. Inparticular, when wet gel is used as the gel, it is preferred that thesolvent removal process be implemented. This process may be carried outin the same manner as the below-described drying treatment.

[Process B]

Process B is a process for obtaining a carbon-containing material byapplying a carbon precursor to the gel and carbonizing the obtainedcarbon precursor containing gel.

A gel described with reference to process A can be used as theaforementioned gel. Therefore, either a wet gel or a dry gel may be usedas the gel.

No specific limitation is placed on the carbon precursor, provided iteventually becomes carbon upon carbonization. Therefore, all thematerials containing carbon can be used. Generally organic materials arepreferable.

Among them, in accordance with the present invention, organic polymerscan be used advantageously. Examples of such compounds include polymersor copolymers such as polyacrylonitrile, polyfurfuryl alcohol,polyimides, polyamides, polyurethanes, polyurea, polyphenols (phenolicresins), polyaniline, polyparaphenylene, polyetherimides,polyamidoimides, and acryl copolymers.

Among them, organic polymers having one or more carbon-carbonunsaturated bonds are preferred. Thus, organic polymers having at leastone carbon-carbon double bond and carbon-carbon triple bond arepreferred. Using such organic polymers makes it possible to conductcarbonization easily and reliably. Moreover, a carbon material with theprescribed strength can be formed. Examples of such organic polymersinclude phenolic resins, epoxy resins, polyimides, polystyrene,polysulfone, polyphenyl ether, melamine resins, and aromatic polyamides.Those polymers can be used singly or in combination of two or morethereof. Furthermore, they can be used together with other organicpolymers. In accordance with the present invention, organic polymershaving one or more aromatic rings are especially preferred. For example,at least one of phenolic resins and polyimides can be usedadvantageously.

Furthermore, those organic polymers that do not have an aromatic ring(for example, polyacrylonitrile, acryl copolymers, and the like), but inwhich rings are formed in the course of carbonization and unsaturatedbonds are produced can be also used advantageously. In other words,those organic polymers which do not have carbon-carbon unsaturated bondsbefore carbonization, but in which rings can be induced andcarbon-carbon unsaturated bonds can be produced by carbonization can bealso used advantageously. Among such organic polymers, polyacrylonitrileis especially preferred.

No specific limitation is placed on the method for the preparation of acarbon precursor containing gel by adding a carbon precursor to the gel,provided that the carbon precursor is formed on the 3D-network structureskeleton of an inorganic oxide serving as a carbon precursor. Examplesof methods that can be advantageously used include, (a) a methodcomprising impregnating a wet gel of an inorganic oxide with a carbonprecursor, (b) a method comprising using a monomer capable of forming anorganic polymer or an oligomer, and impregnating a wet gel therewith,then conducting polymerization and producing an organic polymer which isthe carbon precursor, and (c) a method comprising the steps ofproviding, by a vapor phase method, a monomer capable of forming anorganic polymer inside a dry gel of an inorganic oxide, then conductingpolymerization and producing an organic polymer as the carbon precursor.

Specific implementation of the above-described method (a) can involveimpregnating a wet gel with a solution obtained by dissolving a carbonprecursor in a solvent or a dispersion (emulsion and the like) obtainedby dispersing a carbon precursor in a solvent. As a result, the carbonprecursor adheres to the 3D-network structure skeleton and forms acoating thereof. When an organic polymer is used as the carbon precursorand the solution or dispersion thereof is brought into contact with awet gel, the wet gel retains the solution or dispersion inside thereofand the organic polymer remains in the 3D-network skeleton structureafter completion of drying. In this case, the polymer may be physicallyadsorbed by the 3D-network skeleton structure. Furthermore, if the wetgel containing a solution with an organic polymer dissolved therein isimmersed in a poor solvent with respect to the organic polymer, then theorganic polymer will precipitate on the 3D-network skeleton structureand will form the surface portion.

The solvent used in the aforementioned solution or dispersion may beappropriately selected from the well-known solvents according to thetype of the organic polymer. Examples of suitable solvents includewater, alcohols such as methanol, ethanol, propanol, and butanol, andglycols such as ethylene glycol and propylene glycol. Those solvents canbe used singly or in combination or two or more thereof.

No limitation is placed on the concentration of the carbon precursor inthe solution or dispersion, and the specific concentration can beappropriately selected according to the desired amount of the carbonprecursor which is to be provided and the type of the carbon precursor.

Specific implementation of the above-mentioned method (b) can involveimpregnating a wet gel with a solution obtained by dissolving an organiccompound (also including oligomer), which is capable of forming anorganic polymer by polymerization, in a solvent or with a dispersionobtained by dispersing the organic compound in a solvent, conductingpolymerization inside the gel, and producing an organic polymer which isa carbon precursor. With this method, an organic polymer grows insidethe 3D-network structure skeleton. Therefore, a carbon precursorcontaining wet gel which has high resistance to physical dissolution canbe obtained.

A monomer corresponding to the target organic polymer may be used as theaforementioned organic compound. For example, when polyacrylonitrile isto be obtained, acrylonitrile can be used, when polyfurfuryl alcohol isto be obtained, furfuryl alcohol can be used, and when polyaniline is tobe obtained, aniline can be used. Furthermore, when polyimides areproduced by a polycondensation reaction which forms imide rings,anhydrous tetracarboxylic acid compounds and diamine compounds can beused as typical compounds. When polyamides are obtained by apolycondensation reaction which forms amido bonds, dicarboxylic acidcompounds or dicarboxylic acid chloride compounds, and diamine compoundscan be used as typical compounds. When polyurethanes are produced, diolcompounds such as polyols and diisocyanate compounds may be used. Whenpolyurea is obtained, diisocyanate compounds may be used. And whenpolyphenols are obtained, phenol compounds and aldehyde compounds may beused.

The organic polymer in accordance with the present invention preferablyhas one or more carbon-carbon unsaturated bonds. Therefore, organiccompounds that produce such organic polymers can be advantageously used.For example, when the organic polymer is a phenolic resin, examples ofsuitable phenolic compounds include phenol, cresol, resorcinol(1,3-benzene diol), catechol, fluoroglycinol, salicylic acid, andhydroxybenzoic acid. In this case, formaldehyde, acetaldehyde, furfural,paraformaldehyde producing formaldehyde upon heating, and hexamethylenetetramine can be used as aldehyde compounds serving as condensatingagents. Basic catalysts and/or acidic catalysts can be used ascondensation catalysts. Basic catalysts mainly may catalyze the additionreaction of methyol groups and the like, and acidic catalysts mainly maycatalyze the polyaddition condensation reaction of methylene bonds andthe like. For example, typical catalysts for the manufacture of phenolicresins, such as hydroxides of alkali metals such as sodium hydroxide andpotassium hydroxide, carbonates of alkali metals such as sodiumcarbonate and potassium carbonate, amines, and ammonia can be used as abasic catalyst. Examples of acid catalysts that can be used includesulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, aceticacid, and trifluoroacetic acid.

No specific limitation is placed on a solvent for dissolving ordispersing the organic compound, and this solvent may be appropriatelyselected from the well-known solvents according to the type of theorganic compound that will be used. Examples of suitable solventsinclude water, alcohols such as methanol, ethanol, propanol, andbutanol, and glycols such as ethylene glycol and propylene glycol. Thesesolvents may be used singly or in combination of two or more thereof.

No specific limitation is placed on the concentration of the organicsolvent in the solution or dispersion, and this concentration may beappropriately determined according to the type of the organic compoundthat will be used.

No specific limitation is placed on the polymerization method, and thepolymerization can be performed by known methods such as thermalpolymerization, catalytic polymerization, photopolymerization, and thelike.

With the above-mentioned method (c), a monomer that can form an organicpolymer as the carbon precursor is provided in a dry gel of an inorganicoxide by a vapor phase method, followed by polymerization. Morespecifically, this method comprises the steps of preparing a vapor of amonomer of an organic polymer such as the above-mentionedpolyacrylonitrile, polyfurfuryl alcohol, and polyaniline, filling thegel with the vapor, and conducting polymerization. Furthermore, in caseof producing polyphenols, the gel can be filled with a phenol compoundand then with vapor of formaldehyde as a condensing agent, followed bycondensation polymerization. Furthermore, in case of obtainingpolyimides and polyamides, a carboxylic acid compound and a diaminecompound serving as starting materials can be evaporated and a gel canbe filled with the vapors, followed by polycondensation.

No specific limitation is placed on the vapor phase method. For example,typical methods such as chemical vapor deposition (CVD) and physicalvapor deposition (PVD) can be employed. A polymer or a monomer thereforcan be gasified or evaporated by heating with using these methods.

The polymerization method can be carried out in the same manner asdescribed with reference to method (b).

In subsequent carbonization treatment, the carbon precursor containinggel that was thus obtained is subjected to carbonization by conductingheat treatment.

In this case, when a wet gel is used as the gel, the gel is preferablydried prior to carbonization to obtain a dry gel.

Usual drying methods such as natural drying, drying by heating, andvacuum drying, as well as supercritical drying method and freeze dryingmethod can be used for the aforementioned drying. Typically if theamount of solid components in a wet gel is decreased to increase thesurface area of the dry gel and decrease its density, the gel strengthdecreases. Furthermore, when drying alone is conducted, the gel mostoften shrinks under the effect of stresses generated during solventevaporation. In order to obtain a dry gel demonstrating excellent porouscapability from a wet gel, it is preferred that supercritical drying orfreeze drying be used. As a result, shrinkage, that is, densification ofthe gel during drying can be effectively avoided. Even when usual dryingmeans is used for solvent evaporation, shrinkage of the gel duringdrying can be suppressed by using a solvent with a high boiling pointfor reducing the evaporation rate or controlling the evaporationtemperature. Furthermore, shrinkage of the gel during drying can be alsocontrolled by subjecting the surface of the solid components of the gelto water repelling treatment, thereby controlling surface tension.

With the supercritical drying method or freeze drying method, thegas-liquid interface is eliminated and drying can be conducted withoutapplying stresses induced by surface tension to the gel skeleton bychanging the phase state of the solvent from the liquid state.Therefore, shrinkage of the gel during drying can be prevented and aporous body of a dry gel having a low density can be obtained. Inaccordance with the present invention, it is especially preferred thatthe super critical drying method be used.

A solvent which is held by the wet gel can be used as a solvent employedin supercritical drying. Furthermore, it is preferred that, ifnecessary, this solvent be replaced with a solvent which is easy tohandle in supercritical drying. Examples of replacement solvents includealcohols such as methanol, ethanol, and isopropyl alcohol which directlyconvert the solvent into a supercritical fluid, and also carbon dioxideand water. Furthermore, organic solvents such as acetone, isoamylacetate, and hexane, which are easily dissolved by supercritical fluidsthereof may be also used for substitution.

Supercritical drying can be conducted in a pressure vessel such as anautoclave. For example, when the solvent is methanol, drying isconducted by raising the pressure and temperature to a critical pressureof 8.09 MPa or higher and a critical temperature of 239.4° C. or higher,which are the critical conditions for methanol, and then graduallyreleasing the pressure while maintaining a constant temperature. Forexample, when the solvent is carbon dioxide, drying is conducted byraising the pressure and temperature to a critical pressure of 7.38 MPaor higher and a critical temperature of 31.1° C. or higher, and thengradually releasing the pressure from the supercritical state, whilemaintaining a constant temperature, and obtaining a gaseous state. Forexample, when the solvent is water, drying is conducted by raising thepressure and temperature to a critical pressure of 22.04 MPa or higherand critical temperature of 374.2° C. or higher. As for the timenecessary for drying, it may be equal to or longer than that requiredfor the solvent inside the wet gel to be replaced at least one time withthe supercritical fluid.

Carbonization is preferably conducted at a temperature of 300° C. orhigher because carbonization is initiated when the carbon precursor hasa temperature of about 300° C. or higher. From the standpoint ofoperation time efficiency, it is preferred than the temperature be 400°C. or higher. The upper limit of heating temperature can be setappropriately to a temperature less than the melting point of theinorganic oxide of the 3D-network structure skeleton. For example, whensilica is used as the inorganic oxide, the dry gel somewhat shrinks at atemperature of about 600° C., but the shrinkage becomes significant at atemperature of 1000° C. or higher. Therefore, the carbonizationtemperature may be selected at a level allowing for effectivesuppression of shrinkage. In accordance with the present invention, itis especially preferred that carbonization be conducted at a temperatureless than 1000° C. (even better, at a temperature of 800° C. or less).

No specific limitation is placed on the carbonization atmosphere, andcarbonization may be conducted in the air, in an oxidizing atmosphere,in a reducing atmosphere, in an inert gas atmosphere, or in vacuum.However, from the standpoint of possible combustion, it is preferredthat the carbonization be conducted in an atmosphere with a low oxygenconcentration when a high temperature is set. The atmosphere with a lowoxygen concentration in accordance with the present invention means thatthe oxygen concentration in the atmosphere is 0 to 10%. Carbonizationcan be also conducted by a drying method, heating in an inactive gasatmosphere such as nitrogen or argon, or heating in vacuum

Second Method

The second method is a first method further comprising a process forremoving partially or completely the inorganic oxide from thecarbon-containing material or material containing a carbon precursor.

Of the porous bodies, the second method makes it possible to obtainadvantageously a porous body whose inner portion is occupied by aninorganic oxide or empty space or a porous body whose inner portion isoccupied by an empty space. Thus, a porous body whose inner portion isoccupied by an inorganic oxide or empty space can be obtained bypartially removing the inorganic oxide. If the entire inorganic oxide isremoved, a porous body can be obtained in which the substantially entireinner portion is occupied by an empty space.

A process for removing the inorganic oxide will be described below. Withthe second method, the inorganic oxide is removed partially orcompletely from the carbon-containing material or a carbon precursorcontaining material. Those removal processes may be implemented at anystage of the first method. Thus, the present invention includes a methodby which the inorganic oxide is removed partially or completely from thecarbon-containing material obtained in process A, a method by which theinorganic oxide is removed partially or completely from the carbonprecursor containing material which is produced in process B and thematerial obtained is then carbonized, and a method by which theinorganic oxide is removed partially or completely from thecarbon-containing material obtained by carbonization in process B.

No limitation is placed on the method for removing the inorganic oxide.For example, any of the well-known methods including evaporation,sublimation, and dissolution can be used. In particular, in accordancewith the present invention, it is preferred that this process beimplemented under mild temperature conditions at which little effect isproduced on the gel skeleton. Therefore, removal by dissolution ispreferred.

Immersion in a solution that will dissolve the inorganic oxide may beemployed as the dissolution method. Solutions of acids or bases can beadvantageously used for the solution employed in the process. In mostcases the gel of an inorganic oxide formed by the sol-gel method has lowcrystallinity and is amorphous. For this reason, it has high solubilityin strong acids and bases. Furthermore, a gel with a 3D-networkstructure skeleton which is a fine particle aggregate also has a highsoftening ability (peptizing ability).

Acids and bases can be appropriately selected according to the type ofthe inorganic oxide. For example, when the inorganic oxide is silica,hydrofluoric acid, alkali hydroxides (sodium hydroxide, potassiumhydroxide), and alkali carbonates (sodium carbonate, sodium hydrogencarbonate) can be advantageously used. Those compounds can be used inthe form of an aqueous solution, alcohol solution, and the like. Theconcentration of acids or bases may be appropriately selected accordingto the type of the acid or base used, the type of inorganic oxide, andthe like.

With the second method for removing the inorganic oxide, a porous bodycan be obtained which has a specific surface area larger than that ofthe carbon-containing porous body obtained by the first method. In the3D-network structure skeleton composed of such a carbon material, ahollow structure is mostly visible in observations with an electronmicroscope or the like. Even when a clear hollow structure is notobserved under an electron microscope, a carbon porous body with a largespecific surface area is still obtained.

The preferred embodiment of the method for the manufacture of anelectron-emitting material in accordance with the present invention willbe described hereinbelow with reference to the drawings.

EMBODIMENT 4

The first method for the manufacture of an electron-emitting materialcomposed of a carbon-containing porous body is composed of basic stepsshown in FIG. 4. Those basic steps include forming a 3D-network skeletonstructure (gel structure: FIG. 4-{circle around (2)}) from a preparedsol solution (FIG. 4-{circle around (1)}) by using a sol-gel method,then forming a carbon precursor on the skeleton surface of the wet geland obtaining a porous body comprising a carbon precursor (compositeporous body) (FIG. 4-{circle around (3)}), and carbonizing the carbonprecursor coated on the skeleton surface to convert it into carbon (FIG.4-{circle around (4)}).

Thus, the method comprises the following steps: synthesizing a wet gelof an inorganic oxide from starting materials of the inorganic oxide,obtaining a carbon precursor containing wet gel by forming the carbonprecursor in a liquid phase in the wet gel of the inorganic oxide thusobtained, then obtaining a composite dry gel by drying the carbonprecursor containing wet gel, and then obtaining a carbon-containingporous body by carbonization. Those steps are basic steps of theprocess. Treatment processes such as solvent substitution, catalyticformation, and surface treatment may be appropriately carried out forimplementing those steps.

According to this manufacturing method, the 3D-network skeletonstructure composed of an inorganic oxide serves as a support forsuppressing shrinkage during carbonization when the carbon precursor iscarbonized. Therefore, shrinkage of the carbon precursor in the courseof carbonization can be suppressed or prevented. As a result, theincrease in density during formation of a carbon coating by the carbonprecursor can be suppressed and the decrease in specific surface areacan be suppressed.

EMBODIMENT 5

The second method for the manufacture of an electron-emitting materialcomposed of a carbon-containing porous body is composed of basic stepsshown in FIG. 5. According to this method, a dry gel of an inorganicoxide having a 3D-network skeleton is provided with a carbon material bya vapor phase method.

Thus, a carbon-containing porous body is obtained by a method comprisingthe steps of preparing a wet gel of an inorganic oxide (FIG. 5-{circlearound (2)}) from a starting material of an inorganic oxide (FIG.5-{circle around (1)}), obtaining a dry gel of the inorganic oxide (FIG.5-{circle around (3)}) by drying the wet gel thus obtained, and forminga carbon-containing material by a vapor phase reaction on the skeletonsurface of the dry gel (FIG. 5-{circle around (4)}). Those steps arebasic steps of the process. Well-known treatment processes such assolvent substitution, catalytic formation, and surface treatment may beappropriately carried out for implementing those steps.

In addition to a method of providing a carbon precursor by a vapor phasereaction and then conducting carbonization, a method of directly forminga carbon material by a vapor phase reaction can be used as a method forforming a carbon-containing material in a vapor phase. In accordancewith the present invention, any of those methods may be used.

According to this manufacturing method, the 3D-network skeletonstructure composed of an inorganic oxide serves as a support for holdingthe aforementioned structure when a carbon-containing coating is formed.As a result, shrinkage during carbon coating formation can besuppressed. Therefore, the increase in density of the carbon compositethat will be obtained is suppressed and the decrease in specific surfacearea can be suppressed. In particular, this method is advantageousbecause when a carbon material is directly provided in a vapor phase,strains such as shrinkage caused by carbonization of carbon precursorcan be avoided.

EMBODIMENT 6

The first method for the manufacture of an electron-emitting materialcomposed of a hollow carbon porous body is composed of basic steps shownin FIG. 6. Those steps include forming a 3D-network skeleton structure(FIG. 6-{circle around (2)}) of an inorganic oxide from a sol solution(FIG. 6-{circle around (1)}), then providing the skeleton surface of thewet gel with a carbon-precursor and manufacturing a carbon-containingporous body (FIG. 6-{circle around (3)}), preparing a dry gel of thecarbon precursor by removing partially or completely the inorganic oxidefrom the carbon-type porous body (FIG. 6-{circle around (4)}), and thencarbonizing the carbon precursor of the hollow structure to convert itinto carbon (FIG. 6-{circle around (5)}).

Thus, the method comprises the following steps: synthesizing a wet gelof an inorganic oxide from starting materials of the inorganic oxide,obtaining a carbon precursor containing wet gel by forming the carbonprecursor in a liquid phase in the wet gel of the inorganic oxide thusobtained, then removing the inorganic oxide from the carbon precursorcontaining wet gel, obtaining a dry gel by drying the carbon precursorcontaining wet gel, and then obtaining a carbon porous body bycarbonization. Those steps are basic steps of the process. Well-knowntreatment processes such as solvent substitution, catalytic formation,and surface treatment may be appropriately carried out for implementingthose steps.

With this method, a 3D-network skeleton is formed from thecarbon-containing material itself, this material being anelectron-emitting component. Therefore, a carbon porous body with alarge specific surface area can be obtained. Furthermore, because theinner portion of the 3D-network skeleton is hollow, further increase inspecific surface area can be achieved. As a result, a carbon porous bodywith a low density and a high specific surface area can be obtained.This material can be used for applications that require a high electronemission capability.

EMBODIMENT 7

The second method for the manufacture of an electron-emitting materialconsisting of a carbon porous body is composed of basic steps shown inFIG. 7. With this method a carbon porous body (FIG. 7-{circle around(5)}) is obtained by partially or completely removing the inorganicoxide from the carbon-containing porous body (FIG. 7-{circle around(1)}˜{circle around (4)}) obtained in the third embodiment or fourthembodiment.

With this method, a 3D-network skeleton is formed from thecarbon-containing material itself, this material being anelectron-emitting component. Therefore, a carbon porous body with alarge specific surface area can be obtained. Furthermore, because theinner portion of the 3D-network skeleton is hollow, a higher specificsurface area can be realized. As a result, a carbon porous body with alow density and a high specific surface area can be provided. Thismaterial can be used for applications that require a high electronemission capability.

(2) Electron-Emitting Element

The electron-emitting element in accordance with the present inventioncomprises: (a) a substrate, (b) a lower electrode layer provided on thesubstrate, (c) an electron-emitting layer provided on the lowerelectrode layer, and (d) a control electrode layer so disposed as not tobe in contact with the electron-emitting layer.

The electron-emitting element in accordance with the present inventionhas the above-described structural elements (a) to (d) and can employelements (a spacer and the like) that have been used in the well-knownelectron-emitting elements, in addition to the electron-emittingmaterial described in section (1) above as an electron-emitting layer.

The substrate can be selected from well-known materials. For example,electrically insulating materials such as glass, quartz, and ceramics(oxide ceramics such as Al₂O₃ and ZrO₂, and non-oxide ceramics such asSi₃N₄, and BN), and electrically conductive materials such aslow-resistance silicon, metals, alloys, and intermetallic compounds canbe also used. No specific limitation is placed on the thickness of thesubstrate, and typically it may be about 0.5 to 2 mm.

No specific limitation is placed on the lower electrode layer, providedit is a material capable of supplying electrons into theelectron-emitting layer. For example, metal materials such as aluminum,titanium, chromium, nickel, copper, gold, and tungsten, and compositematerials obtained by laminating a metal and a low-resistance n-typesemiconductor such as silicon, gallium nitride can be used. Thethickness of the lower electrode layer typically may be about 1 to 50μm.

The material in accordance with the present invention is used for theentire electron-emitting layer or part thereof. This material may be amaterial that emits electrons at least in an electric field. In otherwords, the material in accordance with the present invention may alsoemit electrons under the effect of heat, provided that it emitselectrons in an electric field. The electron-emitting material of onetype or two or more types can be used. Furthermore, electron-emittingmaterials (for example, silicon, metal materials, and the like) otherthan the material in accordance with the present invention may becontained therein.

Moreover, components other than the electron-emitting material may becontained in amounts within a range in which the effect of the presentinvention is not degraded. It is preferred that the material inaccordance with the present invention be contained at 20 vol. % or more(in particular, 50 to 100 vol. %) in the electron-emitting layer. Thethickness of the electron-emitting layer differs depending on type ofthe electron-emitting material used, but typically may be about 0.5 to20 μm.

The material in accordance with the present invention is exposed on thesurface of the electron-emitting layer. When the entireelectron-emitting layer consists of the material in accordance with thepresent invention (electron-emitting material), that is, when theelectron-emitting layer is composed of the material in accordance withthe present invention (electron-emitting material), the material inaccordance with the present invention (electron-emitting material) isobviously exposed on the surface of the electron-emitting layer. On theother hand, when part of the electron-emitting layer comprises thematerial in accordance with the present invention (electron-emittingmaterial), the entire material in accordance with the present invention(electron-emitting material) or part thereof is exposed on the surfaceof the electron-emitting layer. Furthermore, the electron-emitting layerhas electric conductivity, as illustrated by an example in which it iscomposed of carbon.

The electron-emitting layer may be obtained by baking a film of a pastecontaining a powdered electron-emitting material. For example, theprescribed electron-emitting layer can be advantageously obtained bymixing an organic binder (isopropyl methacrylate, or the like) with apowdered electron-emitting material having a mean particle diameter ofabout 0.5 to 10 μm, applying the paste obtained to the lower electrodelayer, and removing the organic binder by baking the film obtained. Thiselectron-emitting layer also can demonstrate the desiredelectron-emitting capability.

The control electrode layer has a function of providing an electricfield to the electron-emitting layer by voltage application andcontrolling the amount of emitted electrons by the intensity of thiselectric field. No limitation is placed on the material therefor,provided it can demonstrate such a function. In particular, metals withgood adhesion to the adjacent layers and having good processability suchas pattern formation ability can be advantageously used. Typicallyaluminum, nickel or the like can be advantageously used. The thicknessof the control electrode layer usually may be about 0.1 to 3 μm.

In the element in accordance with the present invention, any arrangementmay be employed for the electron-emitting layer and the controlelectrode layer, provided that they are not in contact with each other.At least one of an empty space and an electric insulator may beintroduced between the electron-emitting layer and control electrodelayer. For example, the electron-emitting layer provided on thesubstrate may be arranged opposite the control electrode layer via anempty space. More specifically, they can be arranged similarly to a gateelectrode and an emitter in the conventional Spindt-typeelectron-emitting elements. The above-mentioned empty space ispreferably in a vacuum state or a state close thereto. The distancebetween the two layers can be appropriately determined according to thedesired performance, intensity of electric field and the like.Typically, the smaller is this distance, the lower voltage is required.Furthermore, it is preferred that the electron-emitting layer andcontrol electrode layer be arranged substantially parallel to eachother.

The expression “the electron-emitting layer and control electrode layerare not in contact with each other” means that there is a distancebetween the electron-emitting layer and control electrode layer andelectric insulation is provided therebetween, as shown, for example, inthe below-described FIG. 8 and FIG. 9. In Japanese Unexamined PatentPublication No. 2000-285797, which represents an example of prior arttechnology, the electron accelerating layer 101 composed of a poroussilica film and a lead-out electrode 103 are in contact, as shown inFIG. 11. In this prior art, if the material of the electron acceleratinglayer 101 is replaced with an electrically conductive material such ascarbon, then the emitter electrode 102, electron accelerating layer 101and lead-out electrode 103 will be short circuited and the functions ofthe electron-emitting element will be completely lost. In other words,for the electron-emitting element disclosed in this prior art tofunction as an electron-emitting element, the substance (porous silicafilm) constituting the electron accelerating layer 101 has to be anelectrically insulating substance. Therefore, in the prior art, theporous silica film constituting the electron accelerating layer 101cannot be replaced with an electrically conductive material such ascarbon. Furthermore, it should be taken into consideration that in theprior art example (FIG. 11), the electron accelerating layer 101composed of a porous silica film appears to be the component emittingelectrons, but this prior art discloses “the emitter electrode emittingelectrons in an electric field” and, therefore, it is the emitterelectrode 102 which is the component emitting electrons, not theelectron accelerating layer 101 composed of the porous silica film.

The electron-emitting layer and control electrode layer can be disposedindependently from each other. Further, they may be also fixed via aspacer (insulator). Electrically insulating materials such as alumina,zirconia, and silicon dioxide can be advantageously used as the spacer.

The method for the manufacture of the element in accordance with thepresent invention may employ the well-known film fabrication technologyand semiconductor fabrication technology. For example, a sputteringmethod, vacuum deposition method, electron beam deposition method, andchemical vapor deposition method (CVD) can be advantageously used as thefilm fabrication technology.

No specific limitation is placed on the method for forming theelectron-emitting layer, provided that it can be fixed to the lowerelectrode layer located on the substrate. For example, the followingmethods can be employed: (1) a method using an electrically conductiveadhesive to attach the electron-emitting material to the lower electrodelayer provided on a substrate, (2) a method employing coating orprinting a mixture (paste containing the electron-emitting material)obtained by mixing a powder obtained by comminuting theelectron-emitting material with an organic binder on the lower electrodelayer, and (3) a method of fabricating the electron-emitting material onthe lower electrode layer and using it as is as the electron-emittinglayer. Well-known or commercial products can be used for theabove-mentioned electrically conductive adhesive, organic binder, or thelike.

The electron-emitting element in accordance with the present inventioncan be driven by a method similar to that employed with the conventionalelectron-emitting elements. For example, the prescribed voltage may beapplied to the control electrode layer and the lower electrode layerprovided on the substrate. The voltage may be adjusted so that theelectron-emitting layer be in an electric field with an electric fieldintensity of 1×10⁶ V/m or more. In this case, it is typically preferredthat the driving atmosphere be vacuum or a state close thereto.Furthermore, no limitation is placed on the driving temperature, butusually it is preferred that the driving temperature be set to about 0to 60° C. Furthermore, the electric current may be a DC or pulsed(square wave) current.

EMBODIMENT 8

FIG. 8 is a schematic cross-sectional view of the electron-emittingelement in accordance with the present invention. An electron-emittingelement 80 comprises a substrate 81, an electrode layer (lower electrodelayer) 82, an electron-emitting layer 83 for emitting electrons, andinsulator layer 85, and a control electrode layer 84 for applying avoltage (control power source 86) for electron emission, as the basicstructural elements. Here, the electron-emitting layer 83 is composed ofan electron-emitting material explained in relation to the embodimentsor composite materials containing such electron-emitting material.

The electrode layer 82 and the electron-emitting layer 83 are formed onthe substrate 81, and the control electrode layer 84 is disposed via theinsulator layer 85 in the vicinity thereof. As shown in FIG. 8, thecontrol electrode layer 84 was formed so as to surround the upperperiphery of the electron-emitting layer 83, similarly to the gateelectrode in a conventional Spindt-type electron-emitting element, butother implementations are also possible.

In the control electrode layer 84 formed on the insulating layer 85,part of the control electrode layer constituted a “protruding portion87” which protruded from the insulating layer 85. Formation of theprotruding portion is not essential and can be appropriately carried outif necessary. Referring to FIG. 8, a region 88 between the protrudingportion and the electron-emitting layer is an empty space, but it may bealso filled with an insulator.

Typically a glass substrate or quartz substrate can be advantageouslyused as the substrate 81. Furthermore, as described above, alow-resistance silicon substrate and electrically conductive substratesuch as a metal substrate can be also used. When an electricallyconductive substrate is used, the functions of the electrode layer 82can be transferred to the electrically conductive substrate.

The electrode layer 82 is preferably from a metal material such asaluminum, titanium, chromium, nickel, copper, gold, and tungsten, or astructure obtained by laminating a metal and a low-resistance n-typesemiconductor composed of silicon, gallium nitride, or the like. Astructure obtained by laminating the aforementioned electrode layer anda resistive film may be used as the electrode layer 82 in order tostabilize the emission current. Typically it is preferred that thethickness of the electrode layer 82 be about 1 to 50 μm.

A porous body having an electron-emitting component in the skeleton canbe used as the electron-emitting layer 83. A porous body having a finepore size of several tens of nanometers is a representative structure.Furthermore, the electron-emitting layer 83 has a function of emittingelectrons in vacuum under the effect of an electric field generated bythe voltage applied to the control electrode layer 84. The material forthe electron-emitting layer can be appropriately selected from theabove-described materials.

The control electrode layer 84 is a layer having a function of providingan electric field to the electron-emitting layer 83 under appliedvoltage and controlling the amount of emitted electrons by the fieldintensity. This layer is formed on the insulator layer 85. The voltageis applied to the control electrode 84 connected to the positiveelectrode of a power source 86 and the electrode layer 82 connected tothe negative electrode of a power source 86.

Referring to FIG. 8, the electron-emitting layer 83 is disposedadjacently to the control electrode layer 84 via the insulator layer 85,but it is also possible not to use the insulator layer 85, provided thatthe electron-emitting layer 83 and control electrode layer 84 are not incontact with each other.

Because the material in accordance with the present invention is usedfor the electron-emitting layer 83 in the electron-emitting element 80,an electric field concentration effect can be obtained with higherefficiency than in prior art. As a result, the applied voltage can belower than in the conventional configurations.

2. Fluorescent Light-Emitting Element

The fluorescent light-emitting element in accordance with the presentinvention comprises an anode portion having a fluorescent layer and anelectron-emitting element, the anode portion and electron-emittingelement being disposed such that electrons emitted from theelectron-emitting element induce light emission from the fluorescentlayer, and is characterized in that the aforementioned electron-emittingelement is the electron-emitting element of the present invention.

The fluorescent light-emitting element of the present invention uses theelectron-emitting element in accordance with the present invention asthe electron-emitting element. Elements that have been used in thewell-known fluorescent light-emitting elements can be employed as otherelements (container or housing and the like).

A laminate obtained by laminating a fluorescent layer, an anodeelectrode layer, and a substrate in the order of description from theelectron-emitting element can be advantageously used as a basicconfiguration of the anode portion. The configuration of each layer andformation thereof may be within the framework of well-known technology.

When the emitted light is picked up from the front surface (anodeportion), transparent materials that have been used in the well-knownfluorescent light-emitting elements may be used for respective layersconstituting the anode portion. For example, a glass substrate, quartzsubstrate, or the like can be used for the substrate. Indium tin oxide(ITO), tin oxide, zinc oxide, and the like can be used for the anodeelectrode layer.

The fluorescent layer may be appropriately formed according to thedesired color of emission. Thus, the material for the fluorescent layercan be appropriately selected from fluorescent substances (compounds)according to the color which may include three primary colors, red (R),blue (B), and green (G), or intermediate colors. For example, redfluorescent substances such as Y₂O₃ systems and GdBO₃ systems, greenfluorescent substances such as ZnS systems and ZnO systems, and bluefluorescent substances such as Y₂SiO₅ system and ZnS system can be used.As for the formation of the fluorescent layer, it may be formed as athin film, for example, by printing or applying a solution or dispersioncontaining those fluorescent substances on top of the anode electrodelayer.

The arrangement of the electron-emitting layer and anode portion (inparticular, the fluorescent layer) may be such that light can be emitteddue to collision of the electrons emitted from the electron-emittinglayer with the fluorescent layer of the anode portion. It is preferredthat the electron-emitting layer and anode portion (fluorescent layer)be disposed so as to face each other. It is also preferred than an emptyspace (in particular, vacuum) be provided between them. Furthermore, itis desired that the electron-emitting layer and fluorescent layer bedisposed parallel to each other. The distance between theelectron-emitting layer and fluorescent layer can be appropriatelyadjusted according to the desired performance typically within a rangeof from 100 μm to 2 mm.

EMBODIMENT 9

FIG. 9 is a schematic cross-sectional view of the fluorescentlight-emitting element in accordance with the present invention. Thisfluorescent light-emitting element comprises an electron-emittingelement 90, an anode portion 100, and a housing 911 enclosing theaforementioned components as the basic structural elements.

As shown in FIG. 9, the electron-emitting element 90 and anode portion100 are provided independently from the container 911. Alternatively,the anode portion may be directly formed on the inner surface of thehousing. Similarly, the electron-emitting element can be directly formedon the inner surface of the housing. Furthermore, in another possibleimplementation, the electron-emitting element 91 and anode portion 100are pasted together via a spacer, without using a housing, and the spacetherebetween is vacuum or in a state close thereto.

The anode portion 100 may be so disposed that the electrons e⁻ emittedfrom the electron-emitting layer 93 of the electron-emitting element 90effectively are irradiated to with the fluorescent layer 97. As shown inFIG. 9, it is desirable that the fluorescent layer 97 andelectron-emitting layer 93 be so disposed that they face each other viaan empty space, while maintaining a mutually parallel arrangement.

The anode portion 100 has a function of conducting voltage applicationfor accelerating the electrons that were emitted from theelectron-emitting element and inducing light emission from thefluorescent substance. Structural elements thereof include a fluorescentlayer 97/an anode electrode 98 for applying the accelerating voltage toemitted electrons/a front substrate 99. When the emitted light is pickedup from the front substrate 99, ITO which is a transparent conductivefilm typically can be used as the anode electrode 98. Furthermore, glassor the like can be advantageously used as the front substrate 99.

The fluorescent material used in the fluorescent layer 97 may beappropriately selected from a variety of the above-mentioned fluorescentmaterial according to the desired color of emitted light. In this case,it is preferred that a fluorescent material with the highest efficiencybe selected by taking into account the energy value of the emittedelectrons which are accelerated, that is, the anode voltage value.

3. Image Displaying Device

The image displaying device in accordance with the present invention isan image displaying device comprising an anode portion having afluorescent layer and a plurality of two-dimensionally arrangedelectron-emitting elements, in which the anode portion and theelectron-emitting element are so disposed that the electrons emittedfrom the electron-emitting element cause the fluorescent layer to emitlight, wherein the electron-emitting element is the electron-emittingelement in accordance with the present invention.

The image displaying device of the present invention uses theelectron-emitting element in accordance with the present invention as anelectron-emitting element. The elements that have been used inwell-known image displaying devices can be used as other elements (ahousing, a driver for driving, and the like).

A plurality of electron-emitting elements are arranged twodimensionally. Thus, the electron-emitting elements are arranged in thesame plane and form an array of electron-emitting elements. Aconfiguration having, for example, a plurality of electrode patternswhich are electrically insulated and a plurality of control electrodepatterns so arranged that they are perpendicular to the electrodepatterns (that is, a matrix system) is convenient for such as array fromthe standpoint of manufacturing large-screen devices.

The configuration of the fluorescent layer of the fluorescentlight-emitting element described in the item 2 above can be employed asthe basic configuration of the fluorescent layer. The number of type ofthe fluorescent layer may be appropriately determined according to thenumber of pixels, size of the screen, and the like. The number ofelectron-emitting elements corresponding to one pixel differs dependingon the desired emission brightness, but usually may be about 1 to 50.

In particular, when color images are displayed, individual fluorescentlayers (one pixel) with three primary colors (RGB) as a set may bedisposed on the anode electrode so as to correspond to respectiveelectron-emitting elements. A variety of arrangement methods, e.g.,longitudinal stripes, lateral stripes, and the like, can be employed forarranging the three primary colors. In case of color images, it isusually preferred that the number of electron-emitting elementscorresponding to one pixel be about 1 to 100.

The layout of the anode portion comprising a fluorescent layer and theelectron-emitting elements may be such as to allow for individualcontrol of the amount of light emitted by each fluorescent layer by theelectron emission dose from each electron-emitting element. Inparticular, a configuration is preferred in which the entire fluorescentlayer of the anode portion or part thereof and the electron-emittinglayer of the electron-emitting elements face each other, while aparallel state of the two layers is substantially maintained.

The driving method of the image displaying device in accordance with thepresent invention may be basically identical to that of the conventionalfield emission displays. For example, a drive may be attached to theelectrode layer of electron-emitting elements and the control electrodelayer and the prescribed voltage may be applied to the two layers.

EMBODIMENT 10

FIG. 10 is a cross-sectional perspective view of an image displayingdevice in which a plurality of the electron-emitting elements shown inFIG. 8 or the like are arranged two dimensionally (in this figure, 3rows×3 columns=9) and which comprises a fluorescent layer that emitslight due to irradiation with the emitted electrons.

The method for displaying images with such a configuration is usuallycalled a matrix drive system. The configuration has a lower electrodelayer 102 formed as a band on the substrate 101. Further, the controlelectrode layer 104 for controlling the emission current quantity isformed as a plurality (three in FIG. 10) of bands. Those controlelectrode layers 104 are disposed so as to be perpendicular to the lowerelectrode layer 102, without contact with the lower electrode layer 102.

Drivers 108, 109 for driving are connected to each lower electrode layerand control electrode layer, respectively.

An electron-emitting layer 103 is formed on the lower electrode layer.The electron-emitting layer 103 is preferably disposed so as to be inthe positions of the portions where the lower electrode layer andcontrol electrode layer cross each other.

An anode portion having the same configuration as that of the anodeportion of the fluorescent light-emitting element of the presentinvention is provided above the lower electrode layer 102 and controlelectrode layer 104. The anode portion has a configuration in which afluorescent layer 105, an anode electrode layer 106, and a frontsubstrate 107 are successively laminated in the order of description,starting from the electron-emitting layer.

Referring to FIG. 10, the fluorescent layer 105 constitutes 1 pixel.Therefore, there are a total of 9 electron-emitting layers 109corresponding thereto. Alternatively, the fluorescent layer may becomposed of a plurality of pixels.

If image data is inputted correspondingly to synchronization signals tothe driving drivers 108, 109 when the image displaying device shown inFIG. 10 is driven, the electrons can be emitted with the describedelectron emission dose from the described electron-emitting surface(places where the electrode rows intersect). As a result, in eachelectron-emitting element, the emitted electrons will be accelerated bythe voltage applied to the anode electrode 106 and electrons will beirradiated to the fluorescent layer 105, thereby displaying an image ofany shape and any brightness.

According to the electron-emitting element in accordance with thepresent invention, a specific electron-emitting material is employed forthe electron-emitting layer and the control electrode layer is disposedso as not to be in contact with the electron-emitting layer. Therefore,excellent electric field concentration effect etc. can be achieved.

Furthermore, the aforementioned electron-emitting material can bemanufactured by the manufacturing method in accordance with the presentinvention in a manner easier than that when carbon nanotubes or the likeare employed. Therefore, it is possible to provide an electron-emittingelement which is less expensive than the electron-emitting element usingcarbon nanotubes.

The electron-emitting element in accordance with the present inventionwhich demonstrates the above-described advantages is suitable for theproduction on an industrial scale.

The fluorescent light-emitting element and image displaying device ofthe present invention use the material in accordance with the presentinvention and the electron-emitting element in accordance with thepresent invention. Therefore, products demonstrating performance equalto that of the conventional products or superior thereto can be providedon a massive scale at a lower cost.

INDUSTRIAL APPLICABILITY

The electron-emitting element of the present invention demonstratesperformance equal to that of the conventional products or superiorthereto. Therefore it can be effectively employed in a variety ofelectronic devices using such elements. For example, it can beadvantageously used in fluorescent light-emitting elements, imagedisplaying devices (in particular, field emission displays) and thelike. In the field of image displaying devices, it is suitable for themanufacture of large-screen displays.

EXAMPLES

Specific examples of the electron-emitting material andelectron-emitting element in accordance with the present invention willbe described hereinbelow. The Scope of the present invention is,however, not limited to those examples.

Example 1

A wet gel was prepared by using silica as an inorganic oxide. A startingmaterial liquid was prepared by mixing tetramethoxysilane, ethanol, andaqueous ammonia solution (0.1N) at a respective molar ratio of 1:3:4. Asolid silica wet gel was obtained by pouring the liquid into a mold ofthe prescribed shape and gelling.

Then, a carbon precursor containing wet gel was formed by coating acarbon precursor on the surface of the 3D-network skeleton in the silicawet gel. An aqueous solution of starting materials prepared by usingwater as a solvent and employing resorcinol (0.3 mol/L) formaldehyde,and sodium carbonate at a respective molar ratio of 1:2:0.01 was used asthe carbon precursor. The aforementioned silica wet gel was immersed inthe aqueous solution to impregnate the inside of the gel with thesolution. The gel was then allowed to stay for 2 days at roomtemperature and at about 80° C. As a result, a carbon precursorcontaining wet gel was obtained in which the skeleton surface of thesilica wet gel was coated with a polyphenolic polymer.

Then, the carbon precursor containing wet gel was dried. The dryingtreatment was carried out by replacing the solvent contained inside thewet gel with acetone and conducting supercritical drying. A carbonprecursor containing dry gel was obtained by removing the solventlocated inside. The dry gel was obtained by supercritical drying underthe following conditions: carbon dioxide was used as a drying medium,drying was conducted for 4 hours under a pressure of 12 MPa at atemperature of 50° C., then pressure was gradually decreased, and thetemperature was lowered after the atmospheric pressure was reached. Thesize of the gel was practically the same before and after the drying andalmost no shrinkage was observed. The apparent density was about 220kg/m³ and the porosity was about 90%. Further, a high value of about 800m²/g of specific surface area was determined by measuring with the BETmethod.

Finally, an electron-emitting material composed of a carbon-containingporous body was obtained by carbonizing the carbon precursor containingdry gel. The dry gel was allowed to stay for 1 hour at a temperature of100° C. in a nitrogen atmosphere, then allowed to stay for 1 hour at200° C., allowed to stay for 1 hour at 300° C., allowed to stay for 1hour at 400° C., allowed to stay for 1 hour at 500° C., then thetemperature was inversely reduced at rate of 1 hour at 400° C., 1 hourat 300° C., 1 hour at 200° C., and 1 hour at 100° C., followed bygradual cooling to room temperature. In this process, the size of thedry gel before and after the carbonization was about 90% in thelongitudinal direction. The apparent density was about 300 kg/m³ and theporosity was about 80%. A high value of about 450 m²/g of specificsurface area was determined by measuring with the BET method.

The electron-emitting material (size: length about 2 mm, width about 2mm, height about 1 mm) fabricated in the above-described manner wasattached via an electrically conductive paste (trade name: GraphitePaste) to a metal electrode and the assembly was placed in a vacuumcontainer. An anode electrode was then placed in a position about 1 mmabove the electron-emitting material. The emission current intensity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material (morespecifically, a carbon material fabricated by a similar process (aprocess of coating a carbon precursor and a heating process) on a metalsubstrate) that was not provided with pores and an emission currentdensity of about 40 mA/cm² was obtained with respect to an anode voltageof about 3 kV.

Example 2

A dry gel was obtained by preparing a silica wet gel under the sameconditions as in Example 1 and conducting drying of the gel in the samemanner as in Example 1. A carbon-containing porous body was obtained byplacing the silica dry gel into a quartz tubular furnace, causingpropylene to flow therethrough at a temperature of about 800° C., andproviding the surface of a porous skeleton with a carbon material in avapor phase. Observations of the carbon-containing porous body thusobtained confirmed that a carbon film reaching the inside of theskeleton of the silica dry gel was formed. The size of the dry gel afterthe formation of carbon film was about 85% in the longitudinaldirection, thereby confirming that shrinkage was suppressed.Furthermore, the apparent density was about 350 kg/m³ and the specificsurface area demonstrated a high value of about 450 m²/g.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current was thenmeasured by applying a voltage between the metal electrode and a controlelectrode. As a result, it was found that the emission current wasincreased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 40 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 3

A carbon precursor containing wet gel was prepared under the sameconditions as in Example 1. A wet gel thus obtained was immersed inhydrofluoric acid for 30 minutes at room temperature to obtain a wet gelcomposed only of a carbon precursor. A carbon precursor containing drygel was obtained by subjecting the carbon precursor containing wet gelto drying under the same conditions as in Example 1. The size of the gelbefore and after drying was practically the same.

Furthermore, an electron-emitting material composed of a carbon porousbody was then obtained by carbonizing the carbon precursor containingdry gel under the same conditions as in Example 1. The size aftercarbonization shrunk to about 70% of the length, but the apparentdensity was as low as about 100 kg/m³ and a high value of about 800 m²/gof specific surface area was obtained. Observations conducted with anelectron microscope confirmed that the carbon porous body had a hollowstructure.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current quantity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 60 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 4

A carbon body was obtained by immersing the carbon-containing porousbody fabricated in Example 2 in hydrofluoric acid for 30 minutes at roomtemperature and removing the skeleton portion thereof. The apparentdensity of the carbon porous body was as low as about 100 kg/m³ and ahigh value of about 900 m²/g of specific surface area was obtained.Observations conducted with an electron microscope confirmed that thecarbon porous body had a hollow structure. This appears why a highspecific surface area was obtained.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current quantity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 70 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 5

A wet gel in which a gel skeleton was covered with a carbon precursorwas obtained by immersing the silica wet gel fabricated in Example 1 ina 5 wt. % acetonitrile solution of polyacrylonitrile. This gel wassubjected to drying by the same method as described in Example 1.

An electron-emitting material composed of a carbon-containing porousbody was obtained by treating the carbon precursor containing dry gelthus obtained for 2 hours at 200° C., then treating for 2 hours at 400°C., raising the temperature to 600° C., and then decreasing thetemperature to 100° C. The size of the gel after the treatment becameabout 85%, in terms of the length, and shrinkage was confirmed to besuppressed. The apparent density was as low as about 350 kg/m³ and ahigh value of about 450 m²/g of specific surface area was obtained.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current quantity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 40 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 6

The carbon-containing porous body fabricated in Example 5 was immersedin an aqueous solution of sodium hydroxide with pH adjusted to 10 ormore. An electron-emitting material composed of a carbon porous body wasthen obtained by replacing the solvent with acetone and conductingdrying in the same manner as described in Example 1. The size in thelengthwise direction after treatment became about 90%. The apparentdensity was as low as about 120 kg/m³ and a high value of about 800m²/kg of specific surface area was obtained.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current was thenmeasured by applying a voltage between the metal electrode and a controlelectrode. As a result, it was found that the emission current wasincreased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 50 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 7

A polyamic acid synthesized from pyromellitic dianhydride andoxydianiline was used as a carbon precursor. A solution was prepared bydissolving with N-methyl pyrrolidone so that the concentration of thepolyamic acid became 1 wt. %. A wet gel impregnated with the polyamicacid was obtained by immersing the silica wet gel fabricated in Example1 into this solution. The wet gel containing polyamic acid that was thusobtained was imidized and converted into a dry gel by the following twomethods.

With the first method, chemical imidization was carried out by immersingthe wet gel containing polyamic acid in a pyridine solution of aceticanhydride. A polyimide-containing dry gel A was obtained by drying thispolyimide-containing wet gel.

With the second method, a polyimide-containing dry gel B was obtained bydrying the wet gel containing polyamic acid to obtain a dry gel and thenconducting imidization by heating this dry gel in a nitrogen atmosphereat a temperature of 300° C.

The respective carbonized porous bodies were obtained by carbonizing thepolyimide-containing dry gel A and B in a nitrogen atmosphere at atemperature of 600° C. Respective electron-emitting materials composedof carbon porous bodies were obtained by further heating theaforementioned carbon porous bodies at a temperature of 1200° C. andthen evaporating the silica skeleton and enhancing graphitization at atemperature of 2000° C. or higher. Carbon porous bodies could be thusobtained in a similar manner from the dry gels A and B. By contrast withthe carbon films obtained in the above-described examples, the carbonfilm thus obtained had a highly oriented graphitic structure.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current quantity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 90 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 8

An aqueous solution (concentration of silica component in the aqueoussolution is 14 wt. %) with pH 9 to 10 was prepared by conductingelectrodialysis of sodium silicate. After the pH value of the aqueoussolution of silicic acid was adjusted to 5.5, the solution was placed ina container. A solidified silica wet gel was then obtained by gelling atroom temperature. Then, the silica wet gel was subjected tohydrophobization in a 5 wt. % isopropyl alcohol solution ofdimethyldimethoxysilane and a silica dry gel was thereafter obtained byconducting vacuum drying which is a usual drying method. The drying wasconducted under the following conditions: holding for 3 hours at atemperature of 50° C. and a pressure of 0.05 MPa, then reducing pressureto atmospheric pressure and decreasing the temperature. The silica drygel thus obtained had an apparent density of about 200 kg/m³ and aporosity of about 92%. The value of specific surface area measured bythe BET method was about 600 m²/g. The average pore diameter of thesilica dry gel was about 15 nm.

Then a carbon material was formed on the surface of the 3D-networkskeleton of the silica dry gel thus obtained. The silica dry gel wasplaced in an apparatus for film deposition, an electric discharge plasmaof benzene gas was obtained by high-frequency electromagnetic waves witha frequency of 13.56 MHz and a power of 200 W and an electron-emittingmaterial composed of a carbon-containing porous body was obtained byforming a carbon film in the silica dry gel with a temperature adjustedto 200° C. The apparent density of this carbon-containing porous bodywas about 220 kg/m³, and the shrinkage was found to be small.Furthermore, a high value of about 600 m²/g of specific surface area wasobtained according to the BET method.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current quantity wasthen measured by applying a voltage between the metal electrode and acontrol electrode. As a result, it was found that the emission currentwas increased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 40 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 9

After a silica dry gel was prepared by the same method as in Example 8,another carbon material was provided on the surface of the 3D-networkskeleton thereof. The silica dry gel was placed in an apparatus for filmdeposition, plasma of a mixed gas of carbon monoxide and hydrogen wasobtained by microwave radiation with a frequency of 2.45 GHz and a powerof 300 W and an electron-emitting material composed of acarbon-containing porous body was obtained by forming a diamond film inthe silica dry gel at a sample temperature of about 800° C. The apparentdensity of this carbon-containing porous body was about 220 kg/m³, andthe shrinkage was found to be small. Furthermore, a high value of about600 m²/g of specific surface area was obtained according to the BETmethod.

The electron-emitting material fabricated as described above wasattached via an electrically conductive paste to a metal electrode andthe assembly was placed in a vacuum container, in the same manner as inExample 1. An anode electrode was then placed in a space about 1 mmabove the electron-emitting material and emission current was thenmeasured by applying a voltage between the metal electrode and a controlelectrode. As a result, it was found that the emission current wasincreased by one or more orders in magnitude compared to theconventional structure using a similar carbon material that was notprovided with pores as an emitter and an emission current density ofabout 40 mA/cm² was obtained with respect to an anode voltage of about 3kV.

Example 10

In the above-described examples, a carbon material was used as theelectron-emitting component, but it was confirmed that an emissioncurrent higher than that of the conventional structures could besimilarly obtained with electron-emitting materials fabricated bycoating a 3D-network skeleton with a material easily emitting electron,for example, boron nitride and metal compounds (barium oxide and thelike).

In the above-described examples, a silica porous body was used as theelectrically insulating porous skeleton structure, but it was confirmedthat an emission current higher than that of the conventional structurescould be similarly obtained with electron-emitting materials in whichthe 3D-network skeleton was formed from other porous materials forexample alumina.

Further, in the above-described examples, a characteristic induced by anapplied electric field was described as an electron emissioncharacteristic, but the results obtained in evaluating thermionicemission characteristic by heating the electron-emitting materialsobtained in the above-described examples confirmed that a thermionicemission effect could be induced at a temperature lower than that of theconventional structures.

Example 11

A method for the fabrication of the first electron-emitting element 80shown in FIG. 8 will be described below.

A metal film was formed as an electrode layer 82 on one surface of aquartz substrate 81. The metal film was a tungsten film with a thicknessof 2 μm, but the electrode material is not specifically limited to sucha film.

Then, an electron-emitting layer 83 composed of a porous structure wasformed. In the present example, a porous silica layer with a thicknessof about 1 μm was formed by using a sol-gel method. More specifically,an aqueous solution (0.1N) containing tetramethoxysilane, ethanol, andammonia at a molar ratio of 1:3:4 was prepared as a solution containingsilica starting material. Then, after the adequate viscosity has beenattained, this gel starting material solution was spin coated on asample so as to obtain a thickness of 1 μm. In the present example, aporous silica layer with a thickness of about 1 μm was formed, but thisthickness is not limiting. The preferred range for the thickness isgenerally from 0.1 μm to 10 μm, the specific value depending on theelement structure.

Further, the sample obtained by forming the silica wet gel was washed(solution replacement) with ethanol and then a porous silica layercomposed of a dry gel was obtained by conducting supercritical dryingwith carbon dioxide. The supercritical drying conditions were asfollows: 4 hours under a pressure of 12 MPa at a temperature of 50° C.,then pressure was gradually decreased, and the temperature was loweredafter the atmospheric pressure was reached. The porosity of the poroussilica layer composed of the dry gel thus obtained was about 92%. Theaverage pore diameter was estimated to be about 20 nm according to theBET method. Finally, substances that were adsorbed in the porous layerwere removed from the dried sample by conducting annealing at atemperature of 400° C. in a nitrogen atmosphere.

Then, an electron-emitting layer composed of a carbon material wasformed as an electron-emitting component by forming a carbon precursorcomposed of polyimide by the above-described method and conductingbaking at a temperature of about 800° C.

The electron-emitting element 80 with a structure shown in FIG. 8 wasthen fabricated by forming an insulating layer 85 composed of silicadioxide and an upper electrode serving as a control electrode 84 andusing a typical lithography process.

The electron-emitting element 80 fabricated as described above wasplaced in a vacuum container, a voltage was applied between theelectrode layer and the control electrode so that the control electrodeserved as a positive electrode, and an emission current was measured. Asa result, an emission current density of about 80 mA/cm² which was 10 ormore times larger than the conventional value was obtained.

Example 12

A paste containing an electron-emitting material was produced bygrinding the electron-emitting material fabricated in Example 1 andmixing the comminuted material with a binder (isopropyl methacrylate).An electron-emitting element 80 such as shown in FIG. 8 was produced byapplying the paste to the electrode layer by the ink-jet method andbaking to remove the binder.

The electron-emitting element 80 fabricated as described above wasplaced in a vacuum container, a voltage was applied between theelectrode layer and the control electrode so that the control electrodeserved as a positive electrode, and an emission current was measured. Asa result, an emission current density of about 60 mA/cm² which was 10 ormore times larger than the conventional value was obtained.

Example 13

In the above-described examples, electron-emitting elements wereexplained, but fluorescent light-emitting elements with controllablefluorescent emission dose can be obtained by arranging an anode portionhaving a fluorescent layer opposite those elements.

FIG. 9 is a schematic cross-sectional view of the fluorescentlight-emitting element of the present embodiment. The fluorescentlight-emitting element comprises a electron-emitting element 90described in the examples, an anode portion 100, and a vacuum container911 enclosing those two components as the basic structural elements.

In the element structure shown in FIG. 9, the electron-emitting element90 and anode portion 100 are entirely contained in the vacuum container.

In the present example, the anode portion 100 was formed by laminatingtransparent conductive film (ITO) functioning as an anode electrode 98on a front substrate 99 composed of glass and then applying a ZnS-typefluorescent material as a fluorescent layer 97.

The fluorescent light-emitting device fabricated as described above wasplaced in a vacuum container. A voltage was applied between the lowerelectrode and a control electrode, so that the control electrode servedas a positive electrode, thereby emitting electrons from theelectron-emitting element 91 into a vacuum region. At the same time, anaccelerating voltage of 3 kV was applied to the anode electrode 98 andthe emission current and fluorescent emission brightness were measured.The emission current density was 50 mA/cm² and an emission brightness of800 cd/m² or more was obtained.

Example 14

In the present example, the explanation was conducted with respect to asingle electron-emitting element, but it is also applicable to an imagedisplaying device which is capable of displaying images or text byarranging a plurality of such electron-emitting elements to obtain atwo-dimensional configuration and controlling the fluorescent emissiondose for each element.

FIG. 10 is a cross-sectional perspective view of an image displayingdevice in which electron-emitting elements such as shown in FIG. 8 aretwo-dimensionally arranged (in this figure, 3 rows×3 columns=9). Amethod for displaying images by using this configuration is usuallycalled a matrix drive system. Thus, a band-like lower electrode layer102 formed on a substrate 101 and a similar band-like upper electrodeserving as a control electrode layer 104 for controlling the emissioncurrent intensity are disposed along straight lines and respectivedrivers 108, 109 for driving are connected thereto. If image data isinputted in each driver according to synchronization signals, thenelectrons can be emitted in the desired electron emission quantity fromthe desired electron emission surface (places where the electrode rowsintersect). Thus, an image of any desired shape and any desiredbrightness can be rendered by accelerating the emitted electrons invacuum by the voltage applied to the anode electrode 106 in eachelectron-emitting element and illuminating the fluorescent layer 105with the electrons.

1. An electron-emitting element comprising: (a) a substrate, (b) a lowerelectrode layer provided on said substrate, (c) an electron-emittinglayer provided on said lower electrode layer, and (d) a controlelectrode layer so disposed as not to be in contact with saidelectron-emitting layer, wherein said electron-emitting layer comprisesan electron-emitting material for emitting electrons in an electricfield; (1) said electron-emitting material being a porous body having a3D-network structure skeleton, (2) the 3D-network structure skeletonbeing composed of an inner portion and a surface portion, (3) thesurface portion comprising an electron-emitting component, (4) the innerportion being occupied by (i) at least one of an insulating material anda semiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial.
 2. The electron-emitting element according to claim 1, whereinsaid electron-emitting material is exposed on the surface of saidelectron-emitting layer.
 3. The electron-emitting element according toclaim 2, wherein said electron-emitting layer consist of anelectron-emitting material for emitting electrons in an electric field.4. The electron-emitting element according to claim 1, wherein saidelectron-emitting layer has electric conductivity.
 5. Theelectron-emitting element according to claim 1, wherein saidelectron-emitting layer is obtained by baking a coating film of a pastecontaining a powdered electron-emitting material.
 6. Theelectron-emitting element according to claim 1, wherein thesubstantially entire inner portion is composed of an inorganic oxide. 7.The electron-emitting element according to claim 1, wherein thesubstantially entire inner portion is composed of an empty space.
 8. Theelectron-emitting element according to claim 1, wherein theelectron-emitting component is a carbon material.
 9. Theelectron-emitting element according to claim 8, wherein the carbonmaterial has one or more π bonds.
 10. The electron-emitting elementaccording to claim 8, wherein the carbon material contains graphite asthe main component.
 11. A fluorescent light-emitting element comprisingan anode portion having a fluorescent layer and an electron-emittingelement, said anode portion and electron-emitting element being sodisposed that the electrons emitted from said electron-emitting elementcause said fluorescent layer to emit light, wherein saidelectron-emitting element is the element according to claim
 1. 12. Animage displaying device comprising an anode portion having a fluorescentlayer and a plurality of electron-emitting elements disposedtwo-dimensionally, said anode portion and electron-emitting elementsbeing so disposed that the electrons emitted from said electron-emittingelements cause said fluorescent layer to emit light, wherein saidelectron-emitting element is the element claimed in claim
 1. 13. Amethod for manufacturing an electron-emitting material, (1) theelectron-emitting material being a porous body having a 3D-networkstructure skeleton, (2) the 3D-network structure skeleton being composedon an inner portion and a surface portion, (3) the surface portioncomprising an electron-emitting component, (4) the inner portion beingcomposed of (i) at least one of an insulating material and asemiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial, wherein the method comprises a step A of obtaining anelectron-emitting material composed of a carbon-containing material byadding a carbon material to a gel of an inorganic oxide having a3D-network structure skeleton.
 14. The manufacturing method according toclaim 13, further comprising a step of removing the inorganic oxidepartially or entirely from the carbon-containing material.
 15. Themanufacturing method according to claim 13, wherein a dry gel is used asthe gel of the inorganic oxide and the step of obtaining a porous bodyas the carbon-containing material by adding a carbon material to the drygel is implemented as the step A.
 16. The manufacturing method accordingto claim 13, wherein the carbon precursor contains an organic polymer.17. The manufacturing method according to claim 14, wherein a carbonprecursor contains an organic polymer.
 18. The manufacturing methodaccording to claim 16, wherein the organic polymer has one or morecarbon-carbon unsaturated bonds.
 19. The manufacturing method accordingto claim 16, wherein the organic polymer has one or more aromatic rings.20. The manufacturing method according to claim 16, wherein the organicpolymer is at least one of phenolic resins, polyimides, andpolyacrylonitrile.
 21. A method for manufacturing an electron-emittingmaterial, (1) the electron-emitting material being a porous body havinga 3D-network structure skeleton, (2) the 3D-network structure skeletonbeing composed of an inner portion and a surface portion, (3) thesurface portion comprising an electron-emitting component, (4) the innerportion being composed of (i) at least one of an insulating material anda semiinsulating material, (ii) an empty space, or (iii) an empty spaceand at least one of an insulating material and a semiinsulatingmaterial, wherein the method comprises a step B of obtaining anelectron-emitting material composed of a carbon-containing material byadding a carbon precursor to a gel of an inorganic oxide having a3D-network structure skeleton and carbonizing the carbon precursorcontaining gel thus obtained.
 22. The manufacturing method according toclaim 21, further comprising a step of removing the inorganic oxidepartially or entirely from the carbon precursor containing gel.
 23. Themanufacturing method according to claim 21, wherein a wet gel is used asthe gel of the inorganic oxide and a step of obtaining a porous body asthe carbon-containing material by adding a carbon precursor to said wetgel and drying the carbon precursor containing gel thus obtained toobtain a carbon precursor containing dry gel, and then carbonizing saiddry gel is carried out as the step B.
 24. The manufacturing methodaccording to claim 22, wherein a wet gel is used as the gel of theinorganic oxide and a step of obtaining a porous body as thecarbon-containing material by adding a carbon precursor to said wet gel,removing the inorganic oxide partially or entirely from the carbonprecursor containing gel thus obtained, and then carbonizing theobtained material is carried out as the step B.
 25. The manufacturingmethod according to claim 21, wherein the carbon precursor contains anorganic polymer.
 26. The manufacturing method according to claim 22,wherein the carbon precursor contains one or more types of organicpolymer.
 27. The manufacturing method according to claim 25, wherein theorganic polymer has one or more carbon-carbon unsaturated bonds.
 28. Themanufacturing method according to claim 25, wherein the organic polymerhas one or more aromatic rings.
 29. The manufacturing method accordingto claim 25, wherein the organic polymer is at least one of phenolicresins, polyimides, and polyacrylonitrile.